When photographing is performed in a low illumination environment, a dark photograph image is generated and it is thus difficult to perceive the photographed object. In the prior art, a method of manually or automatically increasing an exposure time or increasing a gain of an image sensor in order to generate a photograph image having a similar brightness to a standard brightness in a low illumination environment has been used.
The method of increasing the exposure time causes a blur due to a wobbling of a camera or a subject movement so that a quality of the photograph image is deteriorated. Meanwhile, the method of increasing, the gain of the image sensor increases not only the incidence light but also a noise generated by the image sensor itself, which also causes the quality deterioration of the photograph image.
Therefore, a scheme for acquiring a clear and bright photograph image in a low illumination environment is required.